Sensor networks have numerous applications, such as security, industrial monitoring, military reconnaissance, and biomedical monitoring. In many such applications, it is either inconvenient or impossible to connect the sensors by wire or cable; a wireless network is preferable. Sensor networks may be implemented indoors or outdoors. Seismic sensors, for example, may be used to detect intrusion or movement of vehicles, personnel, or large earth masses.
The detection of vehicles and personnel is more difficult than detecting large signals, as from earthquakes or movement of earth masses. The reliable detection or tracking over large areas thus requires very large numbers of sensitive detectors, spaced closely. Although placing sensor nodes in the environment is relatively easy, and configuring them in a network is manageable, a problem faced by sensor networks is that determining where they are in geographic coordinate locations is difficult and expensive. A wireless network of numerous sensitive, low cost, low-powered sensor stations is more desirable. However, the resulting overhead for channel estimation is usually prohibitive in a wireless sensor network.